In the aerospace industry a number of component parts of vehicles are constructed from resin impregnated graphite materials since such materials have high strength and rigidity properties. For instance, component parts which have curved portions are assembled into larger structure such as wings, and empenage and fusealage panels. While the end product is normally satisfactory, there can be problems of delamination of the final products and the labor content of the manufacturing process is high.
In typical prior art procedures, a number of very thin fabric layers are placed in a die, after impregnation with resin, and the fabric layers are built up to the desired thickness. In many cases, dozens, or even a hundred layers may be necessary in order to build to the appropriate thickness, which can be, for example, up to 2 inches. This is a very time consuming procedure, and there is significant possibility for damage due to the great amount of handling that occurs. Also delamination is a real possibility since there are so many fabric layers, and since the product is so thick it is difficult to obtain uniform resin flow during manufacture.
Standard multilayer, single thickness fabrics are not satisfactory for use in place of the thin single layers since standard multilayer fabrics do not have the capability of smoothly fitting around a small die radius so as to create a final curved surface. In a standard multilayer fabric, a series of discrete layers are woven and then bound together by simply extending some of the warp or filling threads from one layer into the adjacent layer. Each layer is essentially a standard fabric with the same degree of stretch or elongation as any other layer of the structure. When bent around the curve, since both the top and bottom layers have the same elongation the bottom layer will crease or crinkle since the system is restricted to the length of the top layer. For instance, if it is necessary to bend a 0.25 inch fabric so that it will curve 180.degree. around a 6 inch radius, the inside layer will require 9.43 inches of length to complete the curve while the outer layer (having a 1/4 inch greater radius) will require 9.82 inches of length to reach the same position. This differential of 0.39 inches between the two layers will cause the inner layer to squeeze, resulting in wrinkling or creasing, which is unacceptable.
According to the present invention, a method of producing a resin impregnated graphite structure particularly for the aerospace industry, a woven fabric for producing the final resin impregnated structure, and an aerospace resin impregnated graphite final component part are provided, which overcome the disadvantages of the prior art mentioned above. According to the present invention it is possible to minimize the labor input in the construction of the final parts since less layering need be done. Also according to the present invention, since there is less handling there is less possibility of damage being induced by the handling. Further, since fewer layers exist and since there is the possibility of providing more uniform resin flow during construction, the probability of delamination is greatly reduced.
A basic feature of the present feature is utilization of a few relatively thick layers (e.g., each within the range of about 0.25-1.0 inch) to produce the final product, rather than a large number of thin layers. While thick layers are utilized, the thick layers according to the invention will not wrinkle, fold, crease or pleat when bent around even small radiuses during construction, and are entirely suitable for producing final products having curved portions.
According to one aspect of the present invention a woven fabric is provided for producing resin impregnated structural components having high strength and rigidity. The woven fabric comprises: two face and two back warp ends; a plurality of stuffer warp ends between the face and back; binder warp ends interconnecting the face and back warp ends; the binder warp ends selected from the group consisting of aramid, carbon, and black fibers; the face and back warp ends selected from the group consisting of graphite, carbon, PAN, and pitch fibers; and the fabric having a thickness in the range of about 0.25-1.0 inches. The binder warp ends preferably are primarily aramid, while the other warp ends are preferably primarily graphite. Pure carbon fiber inclusions are also provided in central portion of the fabric, the pure carbon fibers having known purity and crystallinity so that the resistivity thereof is well known, and electricity can be supplied to the fibers to provide heat to the interior of the fabric, and thus promote more uniform resin flow.
According to another aspect of the present invention there is provided an aerospace component part of resin impregnated graphite fiber having a relatively short radius curved portion, and composed of one or more resin impregnated cured layers of woven fabric, each layer comprising: two face and two back warp ends; a plurality of stuffer warp ends between the face and back; and binder warp ends interconnecting the face and back warp ends.
According to yet another aspect of the present invention, a method of producing a resin impregnated graphite structure having a curved portion thereof and having high strength and rigidity is provided. The method comprises the following steps: (a) Weaving a fabric having a thickness in the range of about 0.25-1.0 inches and comprising primarily graphite fiber. (b) Impregnating one or more layers of the fabric with resin. (c) Forming the fabric into a desired shape by placing one or more layers of the fabric into a die, bending the fabric around a radius to form a curved portion without wrinkling, folding, creasing, crinkling or pleating of the fabric; and (d) Further treating the impregnated fabric to produce a final resin impregnated graphite structure having a curved portion and high strength and rigidity. The further treating includes the step of heating the fabric, and this is preferably accomplished by providing the pure carbon fiber inclusions discussed above and supplying heat to the interior of the fabric utilizing those pure carbon fibers, either prior to or simultaneously with the application of heat to the fabric from the exterior thereof, to promote uniform resin flow.
It is the primary object of the present invention to provide for the simplified construction of resin impregnated graphite structures, with minimized probability of delamination while retaining capability to form curved portions. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.